Conventionally, as a rotation angle detector, the device is developed into which a magnet fixed to a rotator and magnetic detectors for detecting strength of the magnet are assembled, and, by rotating the rotator with the magnet relatively to the magnetic detection means, the rotation angle is detected, and which is utilized in various fields, for example, engine of vehicle, steering wheel, DC motor, or the like. Especially, the rotation angle detector in which hall elements are used as magnetic detection means, is developed and utilized.
And it is known that, in the magnetic detection means, magnetic strength to be detected is considerably varied by change of temperature or the like. Accordingly, in the rotation angle detector in which such magnetic detection means are utilized, the rotation angle to be detected has been affected by accident error caused by change of temperature or the like. Therefore, the rotation angle detector in which the rotation angle is detected without being affected by the change of temperature or the like, has been proposed.
In Patent document 1, there is proposed a rotation angle sensor including a drive circuit in which drive currents of hall elements are respectively controlled by applying similar constant currents as drive currents to the two hall elements, so that signal ratio of signals detected by each of hall elements is maintained constant.
FIG. 5 shows the drive circuit of the hall elements which are provided in a rotation angle sensor proposed in Patent document 1. As shown in FIG. 5, the hall voltages of the two hall elements 34a and 34b are respectively detected by drive detection circuits 50a and 50b. And the drive detection circuits 50a and 50b respectively comprise hall element drive part 51, hall voltage detection part 52 and detected voltage amplifying part 53.    Patent document 1: Japanese Patent Application Publication Hei11-295022